Process for the production of hydrazine



sunsz TANK,

ANHYDROUS NH3 HIO .Auuvonous NH F-l LTER B. H NICOLAISEN flied June '4,1954 AMMONOLYZER PROCESS FOR THE ERODUCT'ION OF HYDRAZiNE INVENTOR.Bernard H. Nicoloisen ATTO RN EY S SURGE TANK "24 2 2 1 AQUEOUS uuuouaous SURGE TANK Aougous SOLUTION or omvomzms SULFATE AND N H Feb.26, 1957 dm wu so AQUEOUS United States Patent() 2,783,130 PROCESS FORTHE PRODUCTION OF HYDRAZINE Bernard H. Nicolaisen, Kenmore, N. Y.,assignor to Olin Mathieson Chemical Corporation, a corporation ofVirginia Application June 4, 1954, Serial No. 434,522- 1 Claim. (Cl.23-190) My invention relates to improvements in a process for theproduction of anhydrous hydrazine by the ammonolysis of dihydrazinesulfate. My invention 18 particularly directed to a method for therecovery and use of the valuable ammonia and sulfate content of bywhichcan be recycled to the ammonolysis operation,

product ammonium sulfate formed in the production,

Attempts have also been made to prepare anhydrous hydrazine by thereaction of ammonia with hydrazine sulfate. This reaction is highlyexothermic and although partially successful on a small scale isunsatisfactory commercially since the heat liberated is so great thatdecomposition, or at best, sintering of the hydrazine sulfate to asticky mass, results.

An improved commercially feasible process for the production ofanhydrous hydrazine has been disclosed in copending application SerialNo. 99,583 filed June 16, 1949, by Maurice C. Taylor, now U. S. Patent2,680,672, issued June 8, 1954. The process proposed by Taylor comprisesreacting anhydrous dihydrazine sulfate with ammonia while maintaining asubstantial part of the dihydrazine sulfate in the liquid phase duringthe course of the reaction. The ammonolysis can be carried out at atemperature of at least about 40 C.i3 C. The re sultant reaction mixtureis a suspension, the solid phase comprising ammonium sulfate, aby-product of the ammonolysis, and the liquid phase comprising asolution of hydrazine in ammonia. The solid phase of the suspension isremoved by filtration. Distillation of the filtrate recovers ammonia andleaves the desired product, an-

hydrous hydrazine.

This process obviates the difficulty of separating water from hydrazineby employing a material, aqueous dihydrazine sulfate, which can bereadily dehydrated by simple evaporation. In the operation of Taylorsprocess aqueous dihydrazine sulfate may be charged to the vessel inwhich the ammonolysis is to be carried out and then dehydrated byapplying heat and vacuum. The tem perature and degree of vacuum arevadvantageously increased as the dehydration proceeds so that when all ofthe Water is removed, a substantial part of the dihydrazine sulfate willbe in the fused state. Alternatively, anhydrous dihydrazine sulfate canbe maintained in the liquid phase, the condition most favorable forammonolysis, by solution in hydrazine. The ammonolysis operation is thencarried out in the same vessel in which the fusion of the dihydrazinesulfate was accomplished. It is preferred to initiate the reaction withgaseous ammonia and to complete the ammonolysis with liquid ammonia. Thereaction mixture is then filtered and distilled to give a filter cake ofammonium sulfate, ammonia and the product anhydrous hydrazine.

The process proposed by Taylor is, therefore, more eflicient andeconomical than the methods of the prior art in that it producessubstantially quantitative yields of anhydrous hydrazine directly bydistillation of the reaction mixture and also allows for the recovery ofsubstantial amounts of the excess ammonia charged. Some ammonia as wellas all of the sulfate content of the dihydrazine sulfate is lost in theprocess, however, as byproduct ammonium sulfate. My present invention isan improvement in Taylors process in that it provides a method for therecovery and reuse in the preparation of anhydrous hydrazine of theammonia and sulfate content of the previously discarded by-productammonium sul fate. The advantages of my improved process are obvious;none of the reactants need be permanently removed from the reaction zoneexcept as the desired product anhydrous hydrazine.

My invention comprises the steps of treating an ammonium sulfate filtercake, obtained by filtering a reaction mixture from the ammonolysis ofdihydrazine sulfate, with an aqueous solution of hydrazine. Thetreatment is continued until all of the ammonium sulfate has dissolvedto form an aqueous solution containing dihydrazine sulfate and ammonia.Ammonia and anhydrous dihydrazine sulfate are recovered from the abovesolution and recycled to the ammonolysis operation to form moreanhydrous hydrazine. The reactants for the production of anhydroushydrazine are recovered from the above solution by a simpledistillation. Anhydrous ammonia can be recovered overhead and aqueousdihydrazine sullate as a bottom product. The aqueous solution ofdihydrazine sulfate can be evaporated to give the anhydrous salt andcharged to the ammonolyzer. Alternatively, the aqueous solution ofdihydrazine sulfate can be charged to the ammonolyzer directly andevaporated to dryness and fused therein prior to ammonolysis. My newprocess, therefore, returns the entire ammonia and sulfate content ofthe by-product ammonium sulfate to the ammonolysis operation asreactants to produce anhydrous hydrazine.

My invention will be further illustrated by reference to the drawingwhich shows a diagrammatic flow sheet of a process for the production ofanhydrous hydrazine by the ammonolysis of dihydrazine sulfate whichembodies the improvement of this invention.

Fused anhydrous dihydrazine sulfate contained in the ammonolyzer 1 istreated with anhydrous gaseous ammonia from surge tank 2 whilemaintaining the contents of the ammonolyzer at least partially in theliquid phase. When sufiicient gaseous ammonia has been introduced toform liquid hydrazine in the mixture, the temperature of the reactionmixture may be gradually reduced as more ammonia is introduced. When thereaction is substantially complete, a large excess of anhydrous liquidammonia is charged to the ammonolyzer to complete the reaction. Thereaction mixture at this point comprises a dilute solution of hydrazinein anhydrous liquid ammonia containing suspended solid ammonium sulfate.The contents of the ammonolyzer are charged to the filter 3. Thefiltrate, comprising hydrazine in ammonia is taining some ammonia,obtained as a bottoms product I from fractionating column 5, is fed toan atmospheric fractionator 6 in which the residual ammonia is removed,

leaving the product anhydrous hydrazine.

The ammonium sulfate filter cake in filter 3 is now treated by theprocess of my invention. The filter cake is washed in the filter 3 withanhydrous liquid ammonia I .Pzitented Feb. 26, 1957.

from line to remove adsorbed hydrazine, and the washings are added tothe main filtrate. The washed filter cake is then treated by theintroduction of dilute aqueous hydrazine. When the filter cake hasdissolved, the aqueous solution containing dihydrazine sulfate andammonia is charged to fractionating tower 8 through surge tank 7. Thefractionating tower 8 is operated under superatmospheric pressure inorder to obtain anhydrous ammonia overhead. The ammonia is condensed toa liquid and recycled to surge tank 2 for reuse in ammonolyzer 1. Thebottoms product from column 8 comprising a solution of dihydrazinesulfate in water is fed to surge tank 9. The contents of surge tank9 maybe evaporated to dryness and the resultant anhydrous dihydrazine sulfatecharged to ammonolyzer 1 or the aque ous solution from surge tank 9 maybe charged directly to the ammonolyzer and dehydrated and fused therein.

Aqueous solutions containing from about 2 to 60% hydrazine by weight aresuitable for treatment of the ammonium sulfate filter cake. I have foundthat a solution containing about 11% hydrazine is particularly suitable.The holding time required for complete solution of a filter cake,depends on several factors including the amount, temperature andconcentration of the hydrazine solution used. Advantageously theproportion of hydrazine to ammonium sulfate does not exceed thestoichiometric requirement of 2:1. All of the hydrazine is then combinedas dihydrazine sulfate, and when the solution is subsequentlyevaporated, for example, as described in the Taylor process, no freehydrazine is lost with the aqueous vapors. In the process of the presentinvention, an excess over the stoichiometric ratio of hydrazine toammonium sulfate may be used, however, provided adequate means areintroduced for the recovery of excess hydrazine in the aqueous overheadfrom the evaporator. For example, such dilute aqueous hydrazine may becharged to an absorber in which an acid liquor is used as scrubbingliquid or it may be charged to an atmospheric fractionator for therecovery of hydrazine hydrate from more dilute aqueous hydrazine or tothe tower producing the 11% hydrazine solution used initially fortreating the ammonium sulfate. I have found that good results andreasonable holding times can be achieved by using the stoichiometricproportions of 64 parts by weight of hydrazine (e. g. 640 parts of 10%aqueous hydrazine) for each 132 parts of ammonium sulfate filter cakewhen the temperature of the solution is in the preferred range of aboutto 100 C. Solution occurs more rapidly at the higher temperatures of therange, but temperatures above 100 C. are not usually desirable since thevapor pressure of ammonia becomes excessive requiring heavy equipment toprevent loss of ammonia. On the other hand, employing hydrazinesolutions at temperatures less than 20 C. usually requires aninconveniently long hold-up time for complete solution of the ammoniumsulfate. Any suitable means of contacting the filter cake can beemployed, e. g., the dilute aqueous hydrazine may be continuously pumpedthrough the filter at a controlled rate providing adequate contact timeor the filter cake can be contacted batchwise with aqueous hydrazine.

Heat required in the fractionating operations may be supplied from anysuitable source such as a reboiler. Pressures of 150 to 200 p. s. i. g.are sutficient to separate ammonia from an aqueous solution in anhydrousform, e. g., anhydrous ammonia distills overhead at about 26 C. under150 p. s. i. g. pressure. The aqueous solutions of dihydrazine sulfateobtained usually contain about 2025% of the salt by weight.

In a specific example of the preferred method of practicing myinvention, approximately 345 parts of dihydrazine sulfate is fused byheating to a temperature of 130 C. in a pressure vessel fitted with anagitator under a vacuum of about 30 inches of mercury. Ammonia vapor isthen charged to the vessel at a gauge. pressure of 275 '4 pounds persquare inch. As the reaction proceeds, hydrazine is formed and thetemperature is gradually reduced to about 56 C. by passing cooling waterthrough a jacket surrounding the reactor. Additional ammonia is suppliedto the reactor to maintain the above-indicated pressure as rapidly asthe ammonia is absorbed by the liquid. A total of about 100 parts ofammonia vapor is thus added. Thereafter, addition of ammonia vapor isdiscontinued and liquid ammonia (wash liquor from the previousoperation) containing in all about 28 parts of hydrazine, together withsufficient fresh ammonia to make a total of about 800 parts is thenadded to the pressure vessel with continued cooling to bring thetemperature down to about 50 C. Thereafter, the solution is filteredunder its own vapor pressure and the filter cake is washed with 890parts of additional fresh ammonia. The original filtrate and washfiltrate are separately collected and the latter set aside for use inthe succeeding operation. Upon evaporation of the ammonia, the originalfiltrate 'yields about 138 parts of a liquid, which is about 95.8%hydrazine or the equivalent of about 96% of the theoretical possibleyield of anhydrous hydrazine based on the dihydrazine sulfate.

Having obtained an ammonium sulfate filter cake by the above procedure,the process of my invention is carried out as follows. Approximately 100parts by weight of ammonium sulfate filter cake is treated with 430parts of an aqueous solution containing 11% hydrazine by weight. Thesolution at 100 C. is charged to the filter and allowed to remain incontact with the ammonium sulfate until solution is complete. Theresulting solution containing dihydrazine sulfate and dissolved ammoniais charged to a fractionating tower and distilled under a pressure ofabout 200 p. s. i. g. anhydrous ammonia is removed overhead and recycledto the ammonolysis reaction. The still bottoms comprise an aqueoussolution containing about 24% dihydrazine sulfate by weight. Thissolution is evaporated to dryness under vacuum to yield the anhydroussalt which is then charged to an ammonolysis operation to produceanhydrous hydrazine.

It is to be understood that the above example is for illustration onlyand is not to be construed as limiting the scope of my invention.

I claim:

In a process for the production of anhydrous hydrazine which comprisesthe ammonolysis of anhydrous dihydrazine sulfate to produce asuspension, the solid phase comprising ammonium sulfate and the liquidphase comprising a solution of hydrazine in ammonia, filtering thesuspension to remove solid ammonium sulfate, distilling the filtrate toseparate ammonia and anhydrous hydrazine, and recycling the ammonia tothe ammonolysis operation, the improvement which comprises treating thesolid ammonium sulfate with an aqueous solution of hydrazine for a timesufiicient to dissolve the ammonium sulfate and produce an aqueoussolution containing dihydrazine sulfate and ammonia, distilling thesolution to recover ammonia and aqueous dihydrazine sulfate, recyclingthe recovered ammonia to the ammonolysis operation, dehydrating thedihydrazine sulfate by evaporation and employing the resultant anhydrousdihydrazine sulfate in the ammonolysis operation.

OTHER REFERENCES The Chem. of Hydrazine by L. F. Audrieth and B. A. Ogg,1951 ed., page 171. John Wiley and Sons,

Inc., N. Y.

I. W. Mellors: A Comprehensive Treatise on Inorganic and TheoreticalChem, vol. 8, 1929 ed., pages 317 and 326 Longmans, Green and Co., N. Y.

